Well, maybe I'm too dumb to fully understand this (for which I honestly beg your pardon), but how can you prove that you are the author (the creator) of something (artwork, novel, music piece etc.) without a specific license confirming your copyright?
Lets' imagine that I'm not a writer, but I find a nice novel here, on SH, and see that, if edited a little, it has a huge potential. I decide to play dirty, copy that novel to my computer, edit it a bit (or not), and go to a copyright licensing agency, pay for the copyright, then go to a publishing company and publish the book, make profit on it and live happily ever after. Who can say that dirty things like this don't happen? Then the real author of the novel sees it published under another name, they come to me and ask something like "What the heck?", but, oh wait, they can't prove that they are the real creator of the novel 'cause I own the license, and any court will actually believe me, 'cause I have the license, and that guy is no one to the novel I own. Doesn't it seem like a pretty real situation? Who owns the copyright then? The same thing can happen to any artwork posted to be watched freely on Internet, can't it? No, I'm not claiming that it's good or anything, you should ask for an author's permission at least because it's good manners. But it's the same as when you use someone's artwork or photos as a wallpaper for your computer. Do you literally go and ask every artist if you can use their work to put it on your screen? Or will you go and ask Imagine Dragons, for example, for a permission to use their song in your school project? Isn't it the same situation when you take someone's artwork to make it your banner or your book cover? If you don't claim the right for the artwork, and you don't make money on it (which you otherwise must share with the work's owner), then why aren't you allowed to take and use it without the author's permission?
Nope. If he still has either: 1) his files he wrote, 2) his papers he wrote on, 3) the story on some site, 4) I could still go on, but you get the point, he can naturally form a copyright claim which is going to be investigated and if confirmed, the whole license is void because it was earned on stolen goods. The company who issued that licence would get so much shit if the case went to a proper lawyer that it could end them, so they would void the licence as fast as they can, cutting ties with the person.
The investigation starts, the specialists go through the material and judge the date of its making, compares to the reported product and issues a verdict. The case is even simpler and faster if an original author posted a story somewhere. They just take the publication date and compare contents. If they are highly comparable then there's zero discussion, the thief is getting yeeted, sued and so on. Why do you think big companies like for eg. WebNovel have dedicated DMCA and Copyright Departments with highly visible contact info on the site? Exactly for reasons like these. So they can react as quickly as possible without getting too much of bad attention.
And that also includes editing parts of the product, like using something in an image. There were plenty of cases where a small tiny detail in some grand graphic resulted in it being sued, taken down, issued apologies, paid reparations, and other stuff.
In schools lower and at the level of college it's not really being frowned upon, but the moment you set foot at a University, literally every person will scream at you to always use free databases like Freepik, Pixabay, and others when doing projects and stuff so that you don't get into any trouble. It's kinda like when turning into an adult you have to be much warier than when being a kid since it can't be just waved off with "a child wouldn't know".
Copyright is unchangeable. The licence in definition is a lease of the ownership. Someone can use something you made under specific rules and circumstances. Licence never transfers creational copyrights. The licence can state that the product can be considered authored by a person under if made enough changes or stuff. He then has the copyrights to the newly created product in the combination of things that were done by that person.
This is just lots and lots of laws and rules and I don't think there's a need for me to go into details. Those were just some basics.
Summing up. Yes, everything is copyrighted. Yes, it's wrong and "illegal" to use anything without permission (always get written if you can). Yes, people everywhere use everything and always will be. It's not like my avatar is made by me. Due to the low harmfulness of me using it, no one will ever even think about trying to take it down, unless I start publicly claiming it as my own. You are free to use anything you want. You should only always be aware that there are possible consequences. Using something for a cover, even if it's a non-commercial one, can still easily be considered medium or high harmfulness.
God, I haven't written so much shit about this shit since I was actually explaining the case where I sued to my friend.
Ah, and don't forget that there are people who literally live from this. Going all around the internet, finding multiple instances of something under different names, contacting the one which appeared earlier and invite to take action with their help since they deal with the law or own a lawyer company.
